Support "shared" histograms between processes.

base/metrics/histogram_snapshot_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/histogram_snapshot_manager.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram_flattener.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/stl_util.h"
 
 namespace base {
 
 HistogramSnapshotManager::HistogramSnapshotManager(
     HistogramFlattener* histogram_flattener)
     : histogram_flattener_(histogram_flattener) {
   DCHECK(histogram_flattener_);
 }
 
 HistogramSnapshotManager::~HistogramSnapshotManager() {
   STLDeleteValues(&logged_samples_);
 }
 
-void HistogramSnapshotManager::PrepareDeltas(
-    HistogramBase::Flags flag_to_set,
-    HistogramBase::Flags required_flags) {
-  StatisticsRecorder::Histograms histograms;
-  StatisticsRecorder::GetHistograms(&histograms);
-  for (StatisticsRecorder::Histograms::const_iterator it = histograms.begin();
-       histograms.end() != it;
-       ++it) {
-    (*it)->SetFlags(flag_to_set);
-    if (((*it)->flags() & required_flags) == required_flags)
-      PrepareDelta(**it);
-  }
-}
-
 void HistogramSnapshotManager::PrepareDelta(const HistogramBase& histogram) {
   DCHECK(histogram_flattener_);
 
   // Get up-to-date snapshot of sample stats.
   scoped_ptr<HistogramSamples> snapshot(histogram.SnapshotSamples());
   const std::string& histogram_name = histogram.histogram_name();
-  const uint64_t histogram_id = histogram.name_hash();
+  const uint64_t histogram_hash = histogram.name_hash();
 
   int corruption = histogram.FindCorruption(*snapshot);
 
   // Crash if we detect that our histograms have been overwritten.  This may be
   // a fair distance from the memory smasher, but we hope to correlate these
   // crashes with other events, such as plugins, or usage patterns, etc.
   if (HistogramBase::BUCKET_ORDER_ERROR & corruption) {
     // The checksum should have caught this, so crash separately if it didn't.
     CHECK_NE(0, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     CHECK(false);  // Crash for the bucket order corruption.
   }
   // Checksum corruption might not have caused order corruption.
   CHECK_EQ(0, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
 
   // Note, at this point corruption can only be COUNT_HIGH_ERROR or
   // COUNT_LOW_ERROR and they never arise together, so we don't need to extract
   // bits from corruption.
   if (corruption) {
     DLOG(ERROR) << "Histogram: " << histogram_name
                 << " has data corruption: " << corruption;
     histogram_flattener_->InconsistencyDetected(
         static_cast<HistogramBase::Inconsistency>(corruption));
     // Don't record corrupt data to metrics services.
-    int old_corruption = inconsistencies_[histogram_id];
+    int old_corruption = inconsistencies_[histogram_hash];
     if (old_corruption == (corruption | old_corruption))
       return;  // We've already seen this corruption for this histogram.
-    inconsistencies_[histogram_id] |= corruption;
+    inconsistencies_[histogram_hash] |= corruption;
     histogram_flattener_->UniqueInconsistencyDetected(
         static_cast<HistogramBase::Inconsistency>(corruption));
     return;
   }
 
   HistogramSamples* to_log;
   std::map<uint64_t, HistogramSamples*>::iterator it =
-      logged_samples_.find(histogram_id);
+      logged_samples_.find(histogram_hash);
   if (it == logged_samples_.end()) {
     to_log = snapshot.release();
 
     // This histogram has not been logged before, add a new entry.
-    logged_samples_[histogram_id] = to_log;
+    logged_samples_[histogram_hash] = to_log;
   } else {
     HistogramSamples* already_logged = it->second;
     InspectLoggedSamplesInconsistency(*snapshot, already_logged);
     snapshot->Subtract(*already_logged);
     already_logged->Add(*snapshot);
     to_log = snapshot.get();
   }
 
   if (to_log->TotalCount() > 0)
     histogram_flattener_->RecordDelta(histogram, *to_log);
 }
 
 void HistogramSnapshotManager::InspectLoggedSamplesInconsistency(
       const HistogramSamples& new_snapshot,
       HistogramSamples* logged_samples) {
   HistogramBase::Count discrepancy =
       logged_samples->TotalCount() - logged_samples->redundant_count();
   if (!discrepancy)
     return;
 
   histogram_flattener_->InconsistencyDetectedInLoggedCount(discrepancy);
   if (discrepancy > Histogram::kCommonRaceBasedCountMismatch) {
     // Fix logged_samples.
     logged_samples->Subtract(*logged_samples);
     logged_samples->Add(new_snapshot);
   }
 }
 
 }  // namespace base